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  • How do you pass a generic delegate argument to a method in .NET 2.0 - UPDATED

    - by Seth Spearman
    Hello, I have a class with a delegate declaration as follows... Public Class MyClass Public Delegate Function Getter(Of TResult)() As TResult ''#the following code works. Public Shared Sub MyMethod(ByVal g As Getter(Of Boolean)) ''#do stuff End Sub End Class However, I do not want to explicitly type the Getter delegate in the Method call. Why can I not declare the parameter as follows... ... (ByVal g As Getter(Of TResult)) Is there a way to do it? My end goal was to be able to set a delegate for property setters and getters in the called class. But my reading indicates you can't do that. So I put setter and getter methods in that class and then I want the calling class to set the delegate argument and then invoke. Is there a best practice for doing this. I realize in the above example that I can set set the delegate variable from the calling class...but I am trying to create a singleton with tight encapsulation. For the record, I can't use any of the new delegate types declared in .net35. Answers in C# are welcome. Any thoughts? Seth

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  • Create Generic Class Instance from Static Method in a Derived Class

    - by user343547
    I have a class in C# with a template and static method similar to class BClass<T> { public static BClass<T> Create() { return new BClass<T>(); } } From this I derive a class and specify a template parameter to the base class class DClass : BClass<int> { } A problem occurs when I try to use the static method to create an instance of D class Program { static void Main(string[] args) { DClass d = DClass.Create(); } } Gives a compiler error "Cannot implicitly convert type 'Test.BClass<int ' to 'Test.DClass'." Adding the below cast leads to a runtime casting exception. DClass d = (DClass)DClass.Create(); Is there any succint way to allow the static method to create instances of the derived class? Ideally I would like the equivalent of a c++ typedef and I don't want the below syntax (which does work). BClass<int> d = DClass.Create();

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  • Type classe, generic memoization

    - by nicolas
    Something quite odd is happening with y types and I quite dont understand if this is justified or not. I would tend to think not. This code works fine : type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, obj>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res And this ones complains type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, _>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res The difference is only the underscore in the dictionary definition. The infered types are the same, but the dynamic cast from r to type 'b exhibits an error. 'this runtime coercition ... runtime type tests are not allowed on some types, etc..' Am I missing something or is it a rough edge ?

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  • Java weird generic return type

    - by drozzy
    Browsing through Guava libraries I saw this weird signature on a readLines method from Files class: public static <T> T readLines(File file, Charset charset, LineProcessor<T> callback) I know a little bit about generics in java, but this baffled me. What does the double T mean here? And why is the first one in angled brackets?

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  • Create generic class instance throws TypeLoadException

    - by Elisa
    My TestLayer class has the namespace: "BLL.Infrastructure.TestLayer" and is inside the assembly: "BLL" public class LayerFactory<T, U> { public static IBaseLayer<T, U> Get() { var obj = Activator.CreateInstance("BLL", "BLL.Infrastructure.TestLayer", new object[] { (IBaseLayer<T, U>)null }); } } When I run the code the Activator throws an TypeLoadException with no more details Thats the concrete class it should create: GenericBaseLayer implements the IBaseLayer. public class TestLayer<T, U> : GenericBaseLayer<MyRequest, MyInfo.ActionType> { public TestLayer(IBaseLayer<MyRequest, MyInfo.ActionType> layer) : base(layer) { } } What do I wrong?

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  • Hibernate not saving foreign key, but with junit it's ok

    - by Leonardo
    Hi All, I have this strange problem. In a J2ee webapp with spring, smartgwt and hibernate, it happens that I have a class A wich has a set of class B, both of them mapped to table A and table B. I wrote a simple test case for testing the service manager which is supposed to do insert, update, delete and everything work as expected especially during insert. In the end I have one record in A and records in B with foreign key to A. But when I try to call the service from the web app, the entity in B are saved without a foreign key reference. I am sure that the service is the same. One thing I noticed is that enabling hibernate logging, seems that when the service is called from the application, one more update is made: insert A insert B update A update B update B (foreign key only) update A <--- ??? update B <--- ??? Instead, when junit test case is run, the update is as follows: insert A insert B update A update B update B (foreign key only) I suppose the latest update is what is causing the erroe, maybe it is overwriting values. Considering that the app is using spring, with the well known mechanism of DAO + Manager, where can I investigate to solve this issue ? Someone told me that the session is not closed, so hibernate would do one more update before release the objects by itself. I am pretty sure that all the configuration hbm, xml, and the rest are fine...but I maybe wrong. thanks

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  • Creating a Group of Groups in Django

    - by Greg
    I'm creating my own Group model; I'm not referring to the builtin Group model. I want each hroup to be a member of another group (it's parent), but there is the one "top" group that doesn't have a parent group. The admin interface won't let me create a group without entering a parent. I get the error personnel_group.parent_id may not be NULL. My Group model looks like this: class Group(models.Model): name = models.CharField(max_length=50) parent = models.ForeignKey('self', blank=True, null=True) order = models.IntegerField() icon = models.ImageField(upload_to='groups', blank=True, null=True) description = models.TextField(blank=True, null=True) How can I accomplish this? Thanks.

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  • Fastest way to check a List<T> for a date

    - by fishhead
    I have a list of dates that a machine has worked on, but it doesn't include a date that machine was down. I need to create a list of days worked and not worked. I am not sure of the best way to do this. I have started by incrementing through all the days of a range and checking to see if the date is in the list by iterating through the entire list each time. I am looking for a more efficient means of finding the dates. class machineday { datetime WorkingDay; } class machinedaycollection : List<machineday> { }

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  • How to design this simple database?

    - by Vafello
    I have 2 tables - one storing user information (id, username, password) and the second one storing information about events (id, name, description, date, username(represents the user who created the event)). I would like to implement 'favourite events' functionality. This would allow the user to store his favourite events and later display them in a list. I am not sure how to implement this in terms of design. I need a simple solution. Something like storing the IDs of favourite events in a field in the user table. I am using mysql and php. Can anyone point me to the right direction?

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  • Generic <T> how cast ?

    - by Kris-I
    Hi, I have a "Product" base class, some other classes "ProductBookDetail","ProductDVDDetail" inherit from this class. I use a ProductService class to make operation on these classes. But, I have to do some check depending of the type (ISBN for Book, languages for DVD). I'd like to know the best way to cast "productDetail" value, I receive in SaveOrupdate. I tried GetType() and cast with (ProductBookDetail)productDetail but that's not work. Thanks, var productDetail = new ProductDetailBook() { .... }; var service = IoC.Resolve<IProductServiceGeneric<ProductDetailBook>>(); service.SaveOrUpdate(productDetail); var productDetail = new ProductDetailDVD() { .... }; var service = IoC.Resolve<IProductServiceGeneric<ProductDetailDVD>>(); service.SaveOrUpdate(productDetail); public class ProductServiceGeneric<T> : IProductServiceGeneric<T> { private readonly ISession _session; private readonly IProductRepoGeneric<T> _repo; public ProductServiceGeneric() { _session = UnitOfWork.CurrentSession; _repo = IoC.Resolve<IProductRepoGeneric<T>>(); } public void SaveOrUpdate(T productDetail) { using (ITransaction tx = _session.BeginTransaction()) { //here i'd like ot know the type and access properties depending of the class _repo.SaveOrUpdate(productDetail); tx.Commit(); } } }

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  • Non-normalized association with legacy tables in Rails and ActiveRecord

    - by Thomas Holmström
    I am building a Rails application accessing a legacy system. The data model contains Customers which can have one or more Subscriptions. A Subscription always belong to one and only one Customer. Though not needed, this association is represented through a join table "subscribes", which do not have an id column: Column | Type | Modifiers -----------------+---------+----------- customer_id | integer | not null subscription_id | integer | not null I have this coded as a has_and_belongs_to_many declarations in both Customer and Subscription class Customer < Activerecord::Base has_and_belongs_to_many :subscriptions, :join_table => "subscribes", :foreign_key => "customer_id", :association_foreign_key => "subscription_id" end class Subscription < Activerecord::Base has_and_belongs_to_many :customers, :join_table => "subscribes", :foreign_key => "subscription_id", :association_foreign_key => "customer_id" end The problem I have is that there can only ever be one customer for each subscription, not many, and the join table will always contain at most one row with a certain customer_id. And thus, I don't want the association "customers" on a Subscription which returns an array of (at most one) Customer, I really do want the relation "customer" which returns the Customer associated. Is there any way to force ActiveRecord to make this a 1-to-N relation even though the join table itself seems to make it an N-to-M relation? --Thomas

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  • Generic JSON parser in .NET / WPF?

    - by niklassaers
    I've read lots of tutorials on how to deserialize a JSON object to an object of a particular using DataContractJsonSerializer. However, I'd like to deserialize my object to a Dictionary consisting of either Strings, Arrays or Dictionaries, such as System.Json does with SilverLight when I say JsonObject.Parse(myJSONstring). Is there an equivalent to System.Json that I can use in my WPF project? (just a short background: I'm fetching JSON objects that have way to much info, and I just want to use a little bit to fill out a String array) Cheers Nik

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  • EntityManager does not update on flush()

    - by Sara
    Java EJB's EntityManager does not update data from a Consumer. A Consumer logs into a shop, buys some stuff and wants to look at his shopping-history. Everything is displayed but his last purchase. If he logs out and in, it shows. I have used JPA to persist buys/purchases (that are mapped to the Consumer)to DB. It seems like purchases from this session can't be detected. Code: public Buys buyItem(Consumer c, int amount) { Buys b = new Buys(); b.setConsumerId(c); b.setContent("DVD"); b.setPrice(amount); em.persist(b); em.flush(); return b; } public Collection getAllBuysFromUser(Consumer consumer) { Collection collection = consumer.getBuysCollection(); return collection; } Help!? Flush does not do the trick...

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  • Java sockets: multiple client threads on same port on same machine?

    - by espcorrupt
    I am new to Socket programming in Java and was trying to understand if the below code is not a wrong thing to do. My question is: Can I have multiple clients on each thread trying to connect to a server instance in the same program and expect the server to read and write data with isolation between clients" public class Client extends Thread { ... void run() { Socket socket = new Socket("localhost", 1234); doIO(socket); } } public class Server extends Thread { ... void run() { // serverSocket on "localhost", 1234 Socket clientSock = serverSocket.accept(); executor.execute(new ClientWorker(clientSock)); } } Now can I have multiple Client instances on different threads trying to connect on the same port of the current machine? For example, Server s = new Server("localhost", 1234); s.start(); Client[] c = new Client[10]; for (int i = 0; i < c.length; ++i) { c.start(); }

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  • Help needed with Linq To Sql Query

    - by fearofawhackplanet
    I have the concept of valid/ordered transitions. So for example, it's not possible to move to status In progress from status Complete. Current and Next in table StatusTransition are FK (StatusType.Id). The Linq generator has created the following relations: Child Property Name: StatusTransitions1 Parent Property Name: StatusType1 Participating Properties: StatusType.Id -> StatusTransition.Next Child Property Name: StatusTransitions Parent Property Name: StatusType Participating Properties: StatusType.Id -> StatusTransition.Current I'm normally ok with Linq but I'm having difficulty getting the list of valid Next StatusTypes from the Current status. public List<StatusType> GetValidStatusTransitions(int statusId) { // trying to write something like the following // (obviously not correct) return _statusRepository .Where(s => s.Id == statusId) .Next.StatusTypes; }

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  • Converting generic type to it's base and vice-versa

    - by Pajci
    Can someone help me with the conversion I am facing in enclosed code ... I commented the lines of code, where I am having problem. Is this even the right way to achieve this ... what I am trying to do, is forward responses of specified type to provided callback. public class MessageBinder { private class Subscriber<T> : IEquatable<Subscriber<T>> where T : Response { ... } private readonly Dictionary<Type, List<Subscriber<Response>>> bindings; public MessageBinder() { this.bindings = new Dictionary<Type, List<Subscriber<Response>>>(); } public void Bind<TResponse>(short shortAddress, Action<ZigbeeAsyncResponse<TResponse>> callback) where TResponse : Response { List<Subscriber<TResponse>> subscribers = this.GetSubscribers<TResponse>(); if (subscribers != null) { subscribers.Add(new Subscriber<TResponse>(shortAddress, callback)); } else { var subscriber = new Subscriber<TResponse>(shortAddress, callback); // ERROR: cannot convert from 'List<Subscriber<TResponse>>' to 'List<Subscriber<Response>>' ... tried LINQ Cast operator - does not work either this.bindings.Add(typeof(TResponse), new List<Subscriber<TResponse>> { subscriber }); } } public void Forward<TResponse>(TResponse response) where TResponse : Response { var subscribers = this.GetSubscribers<TResponse>(); if (subscribers != null) { Subscriber<TResponse> subscriber; Type responseType = typeof (TResponse); if (responseType.IsSubclassOf(typeof (AFResponse))) { // ERROR: Cannot convert type 'TResponse' to 'AFResponse' ... tried cast to object first, works, but is this the right way? var afResponse = (AFResponse)response; subscriber = subscribers.SingleOrDefault(s => s.ShortAddress == afResponse.ShortAddress); } else { subscriber = subscribers.First(); } if (subscriber != null) { subscriber.Forward(response); } } } private List<Subscriber<TResponse>> GetSubscribers<TResponse>() where TResponse : Response { List<Subscriber<Response>> subscribers; this.bindings.TryGetValue(typeof(TResponse), out subscribers); // ERROR: How can I cast List<Subscriber<Response>> to List<Subscriber<TResponse>>? return subscribers; } } Thank you for any help :)

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  • Creating a Type object corresponding to a generic type

    - by Alexey Romanov
    In Java, how can I construct a Type object for Map<String, String>? System.out.println(Map<String, String>.class); doesn't compile. One workaround I can think of is private Map<String, String> dummy() { throw new Error(); } Type mapStringString = Class.forName("ThisClass").getMethod("dummy", null).getGenericReturnType(); Is this the correct way?

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  • Generic calls to OnResetDevice() and OnLostDevice()

    - by bobobobo
    This is kind of a COM question to do with DirectX. So, both ID3DXSprite and ID3DXFont and a bunch of the other ID3DX* objects require you to call OnLostDevice() when the d3d device is lost AND OnResetDevice() when the device is reset. What I want to do is maintain an array of all ID3DX* objects and simply call OnResetDevice() and OnLostDevice() on each whenever the device is lost or reset. However I can't seem to find a BASE CLASS for the ID3DX* classes... they all seem to COM-ually inherit from IUnknown. Is there a way to do this or do I have to maintain separate arrays of ID3DXFont* pointers, ID3DXSprite* pointers, etc?

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  • Circular database relationships. Good, Bad, Exceptions?

    - by jim
    I have been putting off developing this part of my app for sometime purely because I want to do this in a circular way but get the feeling its a bad idea from what I remember my lecturers telling me back in school. I have a design for an order system, ignoring the everything that doesn't pertain to this example I'm left with: CreditCard Customer Order I want it so that, Customers can have credit cards (0-n) Customers have orders (1-n) Orders have one customer(1-1) Orders have one credit card(1-1) Credit cards can have one customer(1-1) (unique ids so we can ignore uniqueness of cc number, husband/wife may share cc instances ect) Basically the last part is where the issue shows up, sometimes credit cards are declined and they wish to use a different one, this needs to update which their 'current' card is but this can only change the current card used for that order, not the other orders the customer may have on disk. Effectively this creates a circular design between the three tables. Possible solutions: Either Create the circular design, give references: cc ref to order, customer ref to cc customer ref to order or customer ref to cc customer ref to order create new table that references all three table ids and put unique on the order so that only one cc may be current to that order at any time Essentially both model the same design but translate differently, I am liking the latter option best at this point in time because it seems less circular and more central. (If that even makes sense) My questions are, What if any are the pros and cons of each? What is the pitfalls of circular relationships/dependancies? Is this a valid exception to the rule? Is there any reason I should pick the former over the latter? Thanks and let me know if there is anything you need clarified/explained. --Update/Edit-- I have noticed an error in the requirements I stated. Basically dropped the ball when trying to simplify things for SO. There is another table there for Payments which adds another layer. The catch, Orders can have multiple payments, with the possibility of using different credit cards. (if you really want to know even other forms of payment). Stating this here because I think the underlying issue is still the same and this only really adds another layer of complexity.

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  • Multiple has_many's of the same model

    - by Koning Baard
    I have these models: Person has_many :messages_form_person, :foreign_key => :from_user_id, :class_name => :messages has_many :messages_to_person, :foreign_key => :to_user_id, :class_name => :messages Message belongs_to :to_person, :foreign_key => :to_user_id, :class_name => :person belongs_to :from_person, :foreign_key => :to_user_id, :class_name => :person And this view: person#show <% @person.messages_to_person.each do |message| %> <%=h message.title %> <% end %> But I get this error: TypeError in People#show Showing app/views/people/show.html.erb where line #26 raised: can't convert Symbol into String Extracted source (around line #26): 23: <%=h @person.biography %> 24: </p> 25: 26: <% @person.messages_to_person.each do |message| %> 27: 28: <% end %> 29: I basicly want that people can send eachother messages. Can anyone help me? Thanks.

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  • C# Generic method type argument inference

    - by CaptainCasey
    Is there any way that I can generalise the type definitions here? Ideally, I'd like to be able to change the type of 'testInput' and have test correctly infer the type at compile time. public static void Run() { var testInput = 3; var test = ((Func<int, int>) Identity).Compose<int,int,int>(n => n)(testInput); Console.WriteLine(test); } public static Func<T, V> Compose<T, U, V>(this Func<U, V> f, Func<T, U> g) { return x => f(g(x)); } public static T Identity<T> (this T value) { return value; }

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  • How to unit test generic classes

    - by Rowland Shaw
    I'm trying to set up some unit tests for an existing compact framework class library. However, I've fallen at the first hurdle, where it appears that the test framework is unable to load the types involved (even though they're both in the class library being tested) Test method MyLibrary.Tests.MyGenericClassTest.MyMethodTest threw exception: System.MissingMethodException: Could not load type 'MyLibrary.MyType' from assembly 'MyLibrary, Version=1.0.3778.36113, Culture=neutral, PublicKeyToken=null'.. My code is loosely: public class MyGenericClass<T> : List<T> where T : MyType, new() { public bool MyMethod(T foo) { throw new NotImplementedException(); } } With test methods: public void MyMethodTestHelper<T>() where T : MyType, new() { MyGenericClass<T> target = new MyGenericClass<T>(); foo = new T(); expected = true; actual = target.MyMethod(foo); Assert.AreEqual(expected, actual); } [TestMethod()] public void MyMethodTest() { MyMethodTestHelper<MyType>(); } I'm a bit stumped though, as I can't even get it to break in the debugger to get to the inner exception, so what else do I check? EDIT this does seem to be something specific to the Compact Framework - recompiling the class libraries and the unit tests for the full framework, gives the expected output (i.e. the debugger stops when I'm going to throw a NotImplementedException).

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  • Generic Open Source REST Client?

    - by Dean J
    I want a simple client that takes a few parameters (Method, URL, Parameters), makes an HTTP request, and shows me the results that were returned. A browser obviously can easily send GET and POST requests, but I have no good ideas on DELETE and UPDATE. Did I miss something in browser 101, or is there a common freeware tool to do this? I've seen other threads that give me Java APIs for a simple client, but that's not what I'm looking for.

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  • Default for generic type?

    - by Mark
    Is it possible to do something like public class PriorityQueue<TValue, TPriority=int> where TPriority : IComparable (note the =int) ? Before you suggest it, yes, I know I can just add another line: public class PriorityQueue<TValue> : PriorityQueue<TValue, int> { } But I'm wondering if it's possible to do it as a param.

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  • Linq to Sql: Generic Stored Procedures

    - by Eric
    Hello everyone, I am using Linq-to-Sql for a C# application and am currently working on some stored procedures. The application is for a newspaper, and a sample stored procedure is the following: ALTER PROCEDURE dbo.Articles_GetArticlesByPublication @publicationDate date AS SELECT * FROM Articles WHERE Articles.PublicationDate=@publicationDate Anyway, this query gets all of the articles where the publication date is equal to the argument (publicationDate). How can I alter this so that the argument can handle multiple publication dates? Also, I'd prefer not to use "BETWEEN," rather, I want to pick and choose dates.

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